The invention relates to an apparatus and method for determining the phase of a motorcycle engine.
Four-stroke internal combustion engines include a piston reciprocating in a cylinder. The piston executes four strokes or phases for each cycle of the engine. The phases are compression, expansion, exhaust, and intake. The piston moves in a first direction during the compression and exhaust strokes, and in a second, opposite direction during the expansion and intake strokes. A spark plug is positioned at least partially in the cylinder""s combustion chamber and is used to ignite a combustible mixture in the combustion chamber near the end of the compression stroke to drive the piston on the subsequent expansion stroke.
In some engines, the spark plug is timed to spark each time the piston approaches or reaches top-dead-center (TDC). Because the piston reaches TDC twice during each cycle, this known arrangement causes the spark plug to activate twice for each cycle, once during the compression stroke and again during the exhaust stroke. During the exhaust stroke, products of combustion are exhausted from the cylinder, and there is no combustible mixture in the combustion chamber. Thus, activating the spark plug during the exhaust stroke is a waste of energy and may reduce the longevity of the spark plug.
It is also known to mount a sensor near the cam shaft of a motorcycle engine to determine the phase of the engine. Because the cam shaft rotates once for each four-stroke cycle of the motorcycle engine, the sensor is able to determine the phase of the engine by sensing the position of the cam shaft (e.g., counting the teeth on a cam gear).
It is also known to mount a crank gear sensor near a crank gear of an engine, and monitor the rotation of the crankshaft to determine the engine phase. For example, in U.S. Pat. No. 5,562,082, a crank gear sensor is used to measure the rotational speed of the crankshaft both before and after one of the pistons reaches TDC in the first rotation of the crankshaft. The disclosed method for measuring the crankshaft speed includes measuring the time it takes for two groups of crank gear teeth to pass the crank gear sensor. One of the groups of teeth passes the crank gear sensor prior to the piston reaching TDC, and the other group passes by the crank gear sensor after the piston has reached TDC. Based on the ratio of the measured rotational speeds, a processor determines the phase of the engine, and activates the appropriate spark plugs at the appropriate times beginning with the second crankshaft rotation.
The present invention is an improvement over the system disclosed in U.S. Pat. No. 5,562,082, and is for use in a two-cylinder uneven firing engine, particularly of the V-twin type. Because the system of U.S. Pat. No. 5,562,082 measures the rotational speed of the crankshaft only before and after top-dead-center (TDC), it misses the opportunity to spark that cylinder during the first rotation of the crankshaft. An engine incorporating a system according to the present invention remedies this problem by measuring the rotational speed of the crankshaft at selected angular positions of the crankshaft. The system compares the measured rotational speeds to determine the engine phase, and activates the appropriate spark plug. In most cases, the spark plug is activated during the first rotation of the crankshaft.
To achieve the above-described function, the present invention provides a motorcycle including a frame and an engine mounted to the frame. The engine includes a housing, a crankshaft mounted for rotation within the housing, first and second (e.g., front and rear, respectively) cylinders, and first and second pistons in the first and second cylinders, respectively. The pistons reciprocate within the cylinders in a four stroke combustion cycle to rotate the crankshaft. A crankshaft velocity sensor is provided and positioned to monitor the rotational speed of the crankshaft. A processor is interconnected with the crankshaft velocity sensor, and is programmed to measure the rotational speed of the crankshaft at selected times during the crankshaft rotation. Based on the measured crankshaft speeds, the processor determines the phase of the engine and sparks the appropriate spark plug during a single rotation of the crankshaft.
Preferably, a crank gear is coupled to (e.g., mounted on) the crankshaft for rotation therewith. Preferably, the crankshaft velocity sensor is a crank gear sensor mounted near the crank gear. The crank gear sensor counts the teeth of the crank gear as the crank gear rotates. The crank gear sensor and the processor measure the time taken by first and second groups of teeth to pass by the crank gear sensor before either piston reaches TDC. The processor compares (e.g., calculates the difference between) the first and second time periods and determines whether the second piston is in the compression or exhaust stroke or phase.
If the difference between the first and second time periods is insufficient to determine engine phase, the processor measures a third time period during which a third group of crank gear teeth pass by the sensor. The third group of crank gear teeth pass by the sensor before the first piston reaches TDC, but after the second piston has reached TDC. The processor then compares the third time period to the second time period to determine the phase of the engine and spark the appropriate spark plug during a single rotation of the crankshaft.
The present invention also provides a method for determining the phase of an engine. The method includes monitoring the rotational speed of the engine""s crankshaft and monitoring the pressure in the intake manifold. At low rpm, the engine phase is determined with a crankshaft velocity sensor as described above. At higher rpm, the engine phase may be determined by monitoring a variable corresponding to the pressure in the air intake manifold. The method includes switching between monitoring the crankshaft velocity and the manifold pressure to determine engine phase depending on the engine speed.
Preferably, the manifold pressure is measured with a pressure sensor mounted on the shared air intake manifold that provides air to the cylinders. The pressure sensor is interconnected with the processor, so that the processor can take air pressure measurements. The processor takes a pressure reading at a selected time during each rotation of the crankshaft. By comparing measured air intake manifold pressures of two or more crankshaft rotations, the processor can determine the phase of the engine and resynchronize the engine.
Alternatively, if the engine includes dedicated or individual throttle bores for the cylinders, a pressure sensor may be mounted on one or more of the bores and sense the manifold pressure associated with a particular cylinder. When the manifold pressure for a cylinder drops below a certain threshold, the processor determines that the piston is executing the intake stroke and resynchronizes the engine. In this case, engine phase synchronization is possible in a single crankshaft revolution.
Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims, and drawings.